In the high pressure fluid transmission pipe line industry, it is common practise to remove a length of the line and replace it with a segment of new pipe. This is done to remove a length of pipe having a defect in its wall or to install new valve equipment and the like. The procedure used involves the utilization of sleeves, identified in the trade by the trade mark `Weld Plus Ends`. Such sleeves are slidably mounted over the junctions of the two sets of aligned adjacent pipe ends. Each encircling sleeve is circumferentially welded at each of its ends to the underlying pipe ends, by means of fillet welds.
Prior to the welding operation, it is necessary to flood that portion of the line under repair with a liquid, to empty it of gases, with the aim of eliminating the risk of explosion attendant therewith. The presence of loading liquid in the pipe line is maintained during the repair operation.
To satisfactorily execute the circumferential fillet welds, it is necessary to heat the pipe wall to the proper welding temperature along the area to be welded. The presence of the loading liquid significantly accelerates the cooling rate of the fillet weld and the adjacent pipe wall. When the cooling rate is too rapid, the pipe steel will form brittle martensitic microstructures along the toe of the circumferential fillet weld. This is undesirable, as the pipe often fails at this point when the line is subjected to stress, for example when there is shifting during freeze/thaw cycles of the soil or when there is external loading applied.
There exists, therefore, a need to address the problem of the deleterious cooling effect of the liquid upon the fillet welding process and to attempt a solution which avoids the disadvantages inherent in the prior art techniques.